Roadmaster Brakepro 9300 Repair
Thought I'd add a little to this issue of failing older Roadmaster Brake-pros for those with this common frustration of a decent basic unit that cycles too much.
I picked up an older Roadmaster Brakepro on Facebook Marketplace in pretty clean condition and was told it was running great. Tested and seemed to run fine. When I got home I realized it was cycling pretty often, like every couple minutes. Realizing this wasn't likely by design, I did some googling and quickly found out this is the common issue with these... Damnit...
Well, I'm not one to give up easily on things like this, especially when I just bought it! I searched for the common areas of leakage. The misleading one mentioned usually is the "magnet" folks talk about. This is possible but really is just an electro magnetic valve, and if you disconnect the airline you'll see it's only used in actuation not standby. So I'd avoid that one when searching. Anyway, I did get very minor leak check (spray soapy water on areas of possible leaking) bubbles on the tank, but not enough to drop pressure and cycle every 3 min or less. I finally isolated the leak to the blowoff valve area on the end of the cylinder. I put soapy water on finger and placed it lightly over the valve opening and it bubbled rapidly like I would expect for such a leak to cycle often. Bingo! Thought it was this valve but quickly realized it's the cylinder itself leaking to the valve. These are unfortunately not rebuildable. The o-rings likely get older and shrink just enough to allow small air to pass.
I tried to condition them with air tool oil, and this actually worked but only a short time. I think my time between cycles went from 3 min. to 20 min. (apparently 10min is the standard.
Next I thought about how I could swell & condition the o-rings with another common chemical in the shop. I grabbed my trusty can of PB blaster and read through the many claims around the label. One was something along the lines of conditioning & revitalizing o-rings. I sprayed a shot in each end of the cylinder by pulling the air hoses off and replacing. I then cycled the cylinder by hand a few times. I've been testing it for about 1 week now every day a few times a day recording the time between cycles and I went from about 3 min. without to about 45 minutes. I find this acceptable and will happily use the unit. The 0-rings have not swollen so bad they bind, in fact they've swollen very little, but just enough to get a reasonable time between cycles. I'll likely have to recondition every year or so, but that's fine with me. Good maintenance for the cylinder regardless.
I had originally thought to add transmission sealer, which does this exact thing, but I'm afraid it may swell the o-rings too much and cause damage with too much interference and resulting in a eroded 0-ring which would leak way worse. Also not confident in it also lubricating such as PB blaster does for them.
Hope this helps someone!
2000 Damon 3980 "Emerald"
1998 Jeep Wrangler Sahara Toad "Olive"